1. Field of the Invention
The present invention relates to a method for detecting and localizing unwanted matter, such as deposited cement, contaminants, etc. internally in a pipe string or tubing, preferably a drilling string of significant longitudinal extent, consisting of drilling pipes, preferably drill collars and a bit at the free outer end thereof, said method being based on dropping a weight body narrower than the bore diameter, down through the pipe string.
Likewise, the invention relates to a device comprising auxiliary means for use upon detecting and localizing cement deposits and other contaminant deposits within pipe strings and tubings having significant length extent and composed of built up pipe sections/pipe lengths/individual pipes.
2. Description of the Related Art
It is very important to have unwanted matter such as deposits and lumps localized and removed, from a pipe string which to a larger or smaller degree clog or throttle the drilling string bore. These bore diameter reducing coating build-ups and deposits result often from previous pumping of cement through the drilling string.
Lumps of contaminating substances from circulated cement slurry could represent a clogging phase if they land in the nozzles of the bit which, thus, become clogged or become so throttled that the circulation within the drilling string is influenced in a negative sense. Therefore, it is usual to xe2x80x9ctripxe2x80x9d (run in and pull out) the drilling string, test the individual pipe sections in storage position in the derrick, and clean the pipe section(s) containing deposits and/or lumps, prior to a new run of the drilling string in the well can be carried out.
A drilling string consists of pipe sections screwed together, each section normally consisting of three pipes or pipe lengths interconnected through screwing. After each time""s use of a drill string, the screw connections between the individual pipe sections (a length of about 30 meters) are unscrewed. The pipe sections are usually not demounted into single pipes, but are stored on board the drilling platform in their full lengths, uppermost engaging supportingly into a finger board up in the derrick, resting with their lower ends on the drill floor. Within the derrick, at the level of the finger board, a person sits in order to drop a ball or another heavy weight body down through each pipe section.
If said weight body falls through the respective pipe section without being stopped, the pipe section is considered to be internally non-clogged and could be used for drilling again at a later point of time without further treatment.
If the weight body, on the other hand, is stopped within a pipe section, this is a sign of the occurrence of internal deposits, and the pipe section has to be cleaned, possibly after having been dismounted into the three pipe lengths thereof. Working in the derrick is associated with elements of risk, and this prior art detecting method is bothersome, troublesome and time-demanding. Each individual pipe section has to be tested no matter what place it took in the drill string.
The method and the device according to the invention allow in most cases, where no deposits occur, that one with certainty can assume that the entire drill string is sufficiently clean without having.to control each and every pipe section.
The method according to the invention distinguishes itself through the use of a sleeve-shaped/tubular indicator body with a smaller lateral measure than the diameter of the drill string bore and which, in situ, from a surface position is dropped down through the drill string, landing at a place further down within the drill string, said place, at a later stage, subsequently to disassembling the drill string, can be determined by testing the individual pipe sections, e.g., through a measure indication from one end of the pipe section to the other, in connection with the tripping in/storage of the individual pipe sections on the drill floor.
The sleeve-shaped/tubular indicator body can be adapted to emit radioactivity, or it may be provided with an active radio chip adapted to be detected by means of a magnetic field established outside that pipe section which at any time is being examined in order to recover the indicator body and determine the place positioned at the highest level, referred to the drill string""s position of use, where deposits occur. Then, at this highest positioned place within the drill string, the deposits have stopped the further movement of the indicator body downwardly within the drill string, and above the determined highest positioned place there are no internal deposits, coatings or other accumulations of cement or mud constituents, formation sand, etc. As soon as one has positionally determined and recovered the indicator body and, thus, localized the pipe section exhibiting deposits, the remaining pipe sections which, thus, were positioned above that place within the drill string where the indicator body was stuck, can be considered as deposit-free internally. These pipe sections do not need any testing and may immediately be stored for subsequent use in the next run of the drill string. On the other hand, pipe sections which occupied positions within the drill string below said recorded deposit""s xe2x80x9chighest placexe2x80x9d, may contain coatings. Therefore, the indicator body is dropped once more down into the remaining part of the drill string.
At one end thereof, the end being the lowermost in the position of use, the indicator body may be formed with an external, conical, downwardly tapering stop portion. A special pipe piece having an externally threaded socket at one end thereof and an internally threaded pin at the other end, is, thus, formed for interconnection with an overlying drill pipe of the drill string and an underlying drill collar of the same. The special pipe piece has a stepped bore comprising two coaxial bore portions passing into each other through a short transition portion connecting the upper bore portion, the diameter thereof agreeing with the bore diameter of the overlying drill pipe, the latter diameter exceeding the diameter of an underlying bore portion which agrees with the diameter of the underlying drill collar. In the transition between the two longitudinal bore portions having different diameters, this special pipe piece has an internal, conical, downwardly tapering seat which is substantially complementary to the external, conical stop portion of the indicator body at the lower end thereof.
The indicator body may, in situations where no deposits exist in the upper pipe sections of a drill string, be adapted to point this out immediately after hauling the special pipe piece up in connection with the drill string""s pulling up (tricing), namely upon inspection of the special pipe piece as the first detecting/localization operation, in order to ascertain whether the indicator body has landed in the seat or not.
In order to remove the indicator body in case it has stopped in an area of deposits, a tool may be used, said tool being lowered down into the pipe section. This hoisting tool may have the form of a U-shaped hoop having somewhat resilient U-hoop legs in the plane of the legs and an upper, heavy web loading the tool with a weight. The tool is hoisted down into the pipe concerned, suspended from a line attached to said web at the central point thereof. Laterally, the free outer ends of the U-hoop legs are directed away from each other. Internally, the indicator body has a circumferential groove in communication with the bore.
Uppermost, the indicator body may be formed with a conical, tapering insertion aperture for guiding said U-hoop-shaped tool and temporary clamping of the two, possibly three oppositely directed free outer ends which, thereafter, resile out into engagement position in the area of said internal circumferential groove, so that the upper faces on said outwardly directed, free outer ends of the U-legs engage in below the downwardly facing face defining the internal circumferential groove from above, whereupon the indicator body can be hoisted up and used once more.
For localizing the pipe section of the disassembled drill string within which the indicator body is positioned immediately, the indicator body may have one of two advantageous embodiments.
In one embodiment, the indicator body is provided with a cord having a small plummet at the outer, free end thereof. The cord has such a length that a portion of it will project out from a pipe section""s end if the indicator body itself has got stuck within a pipe section, irrespective of where in the pipe section the wedging of the indicator body did arise. The cord may e.g. have a length between indicator body and plummet of almost 30 meters.
In a second embodiment, a tubular indicator body according to the invention has a length substantially corresponding to the length of the pipe section, i.e., about 30 meters, a wedging of this long indicator body anywhere in the pipe section concerned will cause an end portion of the tubular indicator body to project out from the upper end. This situation can be recorded as soon as the respective pipe section is in the process of being pulled up. Overlying pipe sections of the pipe string can be considered as deposit-free without any need for internal cleaning.